This invention relates to an aerofoil vane actuation mechanism suitable for a gas turbine engine.
Axial flow compressors and turbines for gas turbine engines comprise axially alternative annular arrays of stator aerofoil vanes and rotary aerofoil blades. In order to improve engine efficiency over a wide range of operating conditions, some of the stator aerofoil vanes may be mounted in such a way that each vane is pivotable, over a limited range, about its longitudinal axis. Typically all of the vanes in at least one annular array are arranged to so pivot.
Pivoting the vanes in this manner permits the flow capacity of the compressor or turbine to be changed, thereby ensuring that the flow capacity is always at an optimum value for the particular operating conditions of the engine.
It is important that all of the vanes in a given annular array pivot simultaneously and to the same degree. One common way of achieving this is to attach each vane in a given annular array to a common actuation ring by means of levers. The actuation ring circumscribes the compressor or turbine casing which contains the vanes. Each vane has a lever attached to it which is also pivotally attached to the actuation ring. Rotation of the ring about the engine axis over a limited circumferential distance provides the desired simultaneous pivoting of the vanes.
Under normal circumstances, such vane actuation mechanisms are highly satisfactory. However if one or more of the vanes in a given array should not pivot due, for instance, to thermal or mechanical deterioration, their actuation levers could be subject to uncontrolled flexure. As well as possibly causing damage to the actuation mechanism, there would also be non-simultaneous actuation of the vanes in the array. Such non simultaneous actuation is highly undesirable since it could result in cyclic fatigue damage of the rotor assembly immediately upstream or downstream of the vanes. This, in turn, could possibly lead to engine failure.
It is our object of the present invention to provide a vane actuation mechanism in which such uncontrolled flexure of the mechanism is substantially avoided.